Efforts towards miniaturization have made great progress from the origin of integrated circuits to the development of micro- and nano-electromechanical systems. Recently, nano/micro-electro mechanical systems (MEMS) have found important uses in medicine, aerospace, and many other fields. The spread of these devices to new markets depends on their reliability and resistance under severe conditions. At present, MEMS can perform a variety of functions in diverse areas and, therefore, have a huge potential market, 4 but they are still limited by their structural properties and are often confined to work under restricted atmospheric conditions involving simple types of interactions and motion. The silicon-based MEMS technology, with its well established manufacturing base, is most popular in moving and bending (with no sliding interactions) types of devices but is ill suited for repeated sliding/rotation due to the poor mechanical and tribological properties of the silicon. When silicon surfaces come into contact, the result is inevitably the premature failure of the device due to excessive wear. Because of its poor tribological properties, silicon is not suited for rubbing or sliding motions between two contacting surfaces, and thus, silicon-based MEMS are not attractive for the development of new micro-systems for deployment in harsh environments or under moderate to heavy wear conditions. Additionally, these devices are not generally applicable where bio-compatibility is required. Extensive studies have been performed to reduce sliding friction and wear at the microscale, with particular attention to self-assembled monolayers and use of vapor-phase lubricants at the contacting interfaces. However, self-assembled monolayers have limited lifetime and do not survive at elevated temperatures, while vapor phase lubricants have a limited supply time with a low reachable maximum temperature.
The quest to overcome these limitations has been on finding an alternative material to silicon, one that not only has better mechanical and tribological properties but also is compatible with the standard MEMS processing techniques and, most importantly, has low intrinsic stress. Silicon carbide (SiC) has shown promise due to its better mechanical and tribological properties over silicon. However, issues remain with regard to the higher synthesis temperatures (<800° C.) for growing better quality crystalline SiC along with stress management, doping, and MEMS processing. A real revolution is represented by the recent introduction of a new material, ultrananocrystalline diamond (UNCD), which has outstanding tribological characteristics and excellent mechanical, chemical, and physical properties along with ease of MEMS fabrication. Although several devices incorporating a UNCD layer have been reported none have provided a stand-alone structural material in a thermal actuator.
To electrically actuate a MEMS device, it has to be electrically conductive. It is well known that UNCD thin films grown by using microwave plasma chemical vapor deposition (MPCVD) can attain almost semi-metallic electrical conductivity (˜143 Ω-1 cm-1) when grown with 20% nitrogen gas in the plasma. The nitrogen-incorporated UNCD (N-UNCD) film still retains good mechanical properties. These properties are significantly better than those of silicon and, therefore, make N-UNCD a promising candidate material for the fabrication of MEMS devices.
Despite excellent mechanical, chemical and electrical properties of diamond, one of the major hurdles in adopting diamond as a MEMS material is intrinsic stress. Particularly in case of nitrogen incorporated ultrananocrystalline diamond (N-UNCD), which has excellent electrical properties needed for the fabrication of electrically actuated MEMS/NEMS, but incorporation dopants causes increase in residual stress and therefore making this material not compatible for the MEMS fabrication.
Robust micro and nano actuators with precise control on displacement arc needed in various applications such as remote micro surgery, putting and placing small amounts of hazardous materials in environmentally harsh conditions. Current micro/nano˜actuators based on silicon are not suitable for such applications due to the limitation on materials properties of silicon.